When someone offers you a hand, you don't then grab their bicep to pull yourself up. Especially if you're only just meeting them for the first time, which it looks like Finn is with Rey. You also shouldn't be weird and stare at their hand for a full second or so before pulling yourself up. Apparently Stormtroopers aren't taught how to behave naturally around others. On top of that, the angle of Rey's arm makes it look like she might be kneeling down at this point. So Finn pulling himself up by her bicep would be even more likely to bring her down as a result. 'How can we make this shot look more dramatic than it is?'